36C25618B0167-00001001.docx

Building 170 Chiller Controls Sequence Chiller Plant Chilled water chiller pump VFD shall be enabled whenever its dedicated water chiller is enabled and run for 5 minutes after chiller is disabled. Each pump VFD is enabled through a dedicated DO and pump speed is set at a fixed speed based on correct flow through the chiller. Each pump VFD status and alarm will be monitored through the VFD integration through the BAS.

Water Chillers shall be enabled based on outside air temperature and chilled water demand through a dedicated DO. Chilled water temperature setpoint is reset through a dedicated AO to the chiller based on outside air temperature. During the occupied period chillers are staged up based on maintaining chilled water (building) temperature setpoint and staged down based on calculated load. Both chillers 1 & 2 will be on whenever the total load exceeds 450 tons. At 450 tons and greater chillers 1 & 2 will run to take advantage of chiller part load performance capability. Chiller 1 turns off below 450 tons, remaining chiller 2 turns off below 225 tons. Chiller 3 will run whenever the calculated load is 225 tons and below or whenever chiller 1 or 2 is off for failure or service and the total load exceeds 450 tons. Water chillers status and alarm are monitored through BACnet integration.

Each water chillers supply and return temperatures are monitored through dedicated AI and insertion temperature sensor. Each water chiller flow is determined by supply and return water differential pressure from DP transmitter at each water chiller. Chilled water (building) load is determined by calculated tonnage based on water chiller flow and chilled water delta T.

The chilled water secondary pumps shall be enabled by a dedicated DO for each pumps VFD whenever the chillers are enabled. Each pumps speed shall be determined by a dedicated AO and pumps speed signal shall be the same for each pump. The secondary pumps VFD status and alarm shall be monitor through the VFD integration to the BAS. Secondary pumps speed shall be determined based on remote differential pressure setpoint in the chilled water supply and return piping.

Chiller tower water pumps shall be enabled through a dedicated DO whenever its chiller is enabled. Tower fan VFD’s shall be enabled through a dedicated DO whenever any chiller is enabled. The tower fan VFD’s speed shall be modulated through a dedicated AO. Fan speeds signals shall be the same for each fan. Tower fan VFD’s status and alarm shall be monitored through VFD integration with the BAS. Tower fans speeds shall be modulated to maintain tower water supply setpoint. Tower water setpoint shall be reset from 85 deg F down to 65 deg F based on the outside air wet bulb.

BAS= Building Automation System VFD= Variable Frequency Drive DO= Digital Output DI= Digital Input AO= Analog Output AI= Analog Input DP= Differential Pressure